Peripheral component interconnect (PCI) backplane connectivity system on chip (SoC)

ABSTRACT

An integrated circuit. The integrated circuit comprises an interconnect communication bus and a plurality of peripheral component interconnect (PCI) multi-function endpoints (MFN-EPs) coupled to the interconnect communication bus, each PCI MFN-EP comprising a multiplexing device, a first address translation unit (ATU), and at least one PCI function circuit, each PCI function circuit comprising another ATU and a plurality of base address registers (BARs).

SUMMARY

In accordance with at least one example of the disclosure, an integratedcircuit includes an interconnect communication bus; and a plurality ofperipheral component interconnect (PCI) multi-function endpoints(MFN-EPs) coupled to the interconnect communication bus. Each MFN-EPincludes an output address translation unit (ATU) configured totranslate to a PCI address an address internal to the integrated circuitand at least one PCI function circuit, wherein the at least one PCIfunction circuit is configured to route communications via theinterconnect communication bus to one of the other MFN-EPs of the IC,wherein the at least one PCI function circuit comprises an input ATUconfigured to translate, to an address internal to the integratedcircuit, a PCI address.

In accordance with at least one example of the disclosure, a method ofcommunicating between different peripheral component interconnect rootcomplexes (PCI RCs) includes reading a plurality of memory regionconfiguration definitions by a processor of a backplane integratedcircuit (IC), wherein each memory region configuration definitionidentifies a size of a memory region, identifies an IC communicativelycoupled to the backplane IC where the memory region is located, andidentifies another IC communicatively coupled to the backplane ICallowed access to the memory region, wherein each IC is communicativelycoupled to a different multi-function endpoint (MFN-EP) of the backplaneIC and, for each IC allowed access to one of the memory regions, writingthe size of the memory region by the processor in a base addressregister (BAR) of a peripheral component interconnect (PCI) functioncircuit of the MFN-EP coupled to the IC. The method further includes,for each IC where a memory region is located, configuring a translationregister of an output address translation unit (ATU) in the MFN-EPcoupled to the IC by the processor with a local address local to thebackplane IC and with an address managed by a PCI RC of the IC and, foreach IC allowed access to one of the memory regions, configuring atranslation register of an input ATU in the PCI function circuit of theMFN-EP coupled to the IC by the processor with a local address local tothe backplane IC wherein the translation register of the input ATU isassociated to the BAR of the PCI function circuit of the MFN-EP.

In accordance with at least one example of the disclosure, an integratedcircuit includes an interconnect communication bus and a plurality ofperipheral component interconnect (PCI) multi-function endpoints(MFN-EPs) coupled to the interconnect communication bus, each PCI MFN-EPcomprising a multiplexing device, a first address translation unit(ATU), and at least one PCI function circuit, each PCI function circuitcomprising another ATU and a plurality of base address registers (BARs).

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a system having a plurality of systems on a chip (SoCs)interconnected by a peripheral component interconnect (PCI) backplaneintegrated circuit (IC) in accordance with various examples;

FIG. 2 shows a PCI backplane IC in accordance with various examples;

FIG. 3 shows a base address register (BAR) structure in accordance withvarious examples;

FIG. 4 shows an input address translation unit (ATU) in accordance withvarious examples;

FIG. 5 shows an output ATU in accordance with various examples;

FIG. 6A shows another system having a plurality of SoCs interconnectedby a PCI backplane IC in accordance with various examples;

FIG. 6B shows another PCI backplane IC in accordance with variousexamples; and

FIG. 7A and FIG. 7B show a flow chart of a method of configuring a PCIbackplane IC in accordance with various examples.

DETAILED DESCRIPTION

Peripheral component interconnect (PCI) is an increasingly importanttechnology for promoting communication between computing devices andperipheral devices. A PCI Express (PCIe) system is a development of anearlier PCI system that relies on a serial communication interface: oneserial line output from a PCIe host and one serial line input to thePCIe host. A PCI root complex (RC) generates transaction requests onbehalf of the PCIe host and manages the PCI address space, translatingbetween the internal addressing used by the PCIe host and the PCIaddress space. To accomplish the translations, the PCI RC may build amemory map that defines relationships between internal addresses of thePCIe host and addresses in the PCI address space.

Emerging automotive applications are being designed to include multiplesystems on a chip (SoCs) that have high communication bandwidths andthat rely upon low latency. Peripheral component interconnect express(PCIe) offers low latency and high throughput communications forconnecting between these SoCs. Challenges are presented, however, intranslating between the independent PCI address spaces of each of theSoCs. Some approaches to interconnecting SOCs with independent PCIaddress spaces involve switches, but these solutions suffer fromdrawbacks. Simple switches resort to cascaded connections that increaselatency when more than two SoCs are interconnected via a PCI backplane.Complex switches obviate cascaded connections but may be prohibitivelyexpensive. Additionally, both simple and complex switching solutionsrely on non-transparent bridge (NTB) ports to translate from the PCIaddress space of one SoC to the PCI address space of another SoC. Theuse of such NTB ports interferes with or prevents the restriction ofmemory access among SoCs—for example, to allow SoC2 to read from apredefined region of SoC1's memory while preventing SoC3 from readingthe same predefined region of SoC1's memory.

The present disclosure teaches a PCI backplane integrated circuit (IC)that provides a cost effective inter-SoC PCI communication device thatsupports the ability of the SoCs to restrict access to their memory. ThePCI backplane IC models SoC hosts as separate functions in PCImultifunction endpoints (MFN-EPs). For a first SoC to communicate to asecond SoC via the PCI backplane IC, the first SoC communicates to afirst PCI function circuit of a first MFN-EP that models the second SoC.The first PCI function circuit of the first MFN-EP communicates via aninterconnect communication bus of the PCI backplane IC with a secondMFN-EP, and the second MFN-EP passes the communication on to the secondSoC. For the first SoC to communicate to a third SoC via the PCIbackplane IC, the first SoC communicates to a second PCI functioncircuit of the first MFN-EP that models the third SoC. The second PCIfunction circuit of the first MFN-EP communicates via the interconnectcommunication bus to a third MFN-EP, and the third MFN-EP passes thecommunication on to the third SoC. For the first SoC to communicate to afourth SoC via the PCI backplane IC, the first SoC communicates to athird PCI function circuit of the first MFN-EP that models the fourthSoC. The third PCI function circuit communicates via the interconnectcommunication bus to a fourth MFN-EP, and the fourth MFN-EP passes thecommunication on to the fourth SoC. For the second SoC to communicate tothe first SoC via the PCI backplane IC, the second SoC communicates to afirst PCI function circuit of the second MFN-EP that models the firstSoC. The first PCI function circuit of the second MFN-EP communicatesvia the interconnect communication bus with the first MFN-EP, and thefirst MFN-EP passes the communication on to the first SoC.

Each MFN-EP includes a plurality of PCI function circuits. Each PCIfunction circuit may be configured to map transactions from the PCIaddress space of its associated SoC indirectly to a PCI address space ofa SoC modeled by that specific PCI function circuit. The MFN-EP furtherincludes an output address translation unit (ATU) to map transactionsfrom other SoCs to the PCI address space of the SoC associated with thatMFN-EP. These mappings provide the PCI backplane IC with the ability torestrict access to PCI memory regions of each of the SoCs as configuredby each of the SoCs.

This solution provides low latency, high throughput, and transparency,wherein the transparency allows SoCs to restrict access to their memoryregions selectively. Because the PCI backplane IC, because it is asingle device produced by a single manufacturer, can be more readilyqualified for use in automobiles than a multi-device solution.

Turning now to FIG. 1, a system 100 is described. In an example, thesystem 100 includes a first system on a chip (SoC) 102 having a firstPCI root complex (RC) 104, a second SoC 106 having a second RC 108, athird SoC 110 having a third RC 112, a fourth SoC 114 having a fourth RC116, and a peripheral component interconnect backplane integratedcircuit (PCI backplane IC) 120. In an example, the PCI backplane IC 120includes a first multifunction endpoint (MFN-EP) 122, a second MFN-EP124, a third MFN-EP 126, a fourth MFN-EP 128, an interconnectcommunication bus 130, a processor 132, and a memory 134. Each of theMFN-EPs 122, 124, 126, 128 is coupled to the interconnect communicationbus 130 by a plurality of communication paths 136. The first RC 104 iscommunicatively coupled to the first MFN-EP 122 by an input line 140 andan output line 142, where the terms “input” and “output” are designatedrelative to the PCI backplane IC 120. The second RC 108 iscommunicatively coupled to the second MFN-EP 124 by an input line 144and an output line 146. The third RC 112 is communicatively coupled tothe third MFN-EP 126 by an input line 148 and an output line 150. Thefourth RC 116 is communicatively coupled to the fourth MFN-EP 128 by aninput line 152 and an output line 154. In an example, each of the lines140-154 is a serial communication line. In another example, each of thelines 140-154 includes a plurality of parallel conductors.

In some contexts, the SoCs 102, 106, 110, 114 may be referred to asremote SoCs or as remote hosts. In an example, one or more of the SoCsof system 100 may be replaced by a processor that is not a system on achip. In an example, the PCI backplane IC 120 may have three MFN-EPsinstead of four MFN-EPs as illustrated. In an example, the PCI backplaneIC 120 may have five or more MFN-EPs instead of four MFN-EPs asillustrated. In an example, the system 100 may be part of an automobile.For example, the SoCs 102, 106, 110, 114 may be remote processors withinthe automobile that communicate with each other via the PCI backplane IC120. One of the SoCs 102, 106, 110, 114 may include a camera sensor andsupport a back-up video functionality of the automobile. One of the SoCs102, 106, 110, 114 may include a radar processor and support radarsensing and ranging functionality of the automobile (e.g., to supportproximity warnings and/or self-driving functionality).

As will be discussed further below, each of the MFN-EPs 122, 124, 126,128 models a plurality of remote SoCs and provides a communicationportal, using that model, to the remote SoCs that it models. Forexample, the first MFN-EP 122 models each of the SoCs 106, 110, 114 asPCI function circuits and provides the first SoC 102 with acommunication portal through which to access the other SoCs 106, 110,114. The modeling of the SoCs 102, 106, 110, 114 provided by MFN-EPs122, 124, 126, 128 promote the transparency to SoCs to restrict accessto their memory based on the SoC attempting to access the memory, asdiscussed further hereinafter. This transparency is desirable in someapplications, for example where a SoC desires to allow one or morespecific other SoC to access its memory but to prohibit another specificSoC from accessing that memory.

The first SoC 102 may complete a transaction involving the second SoC106 by sending a transaction to the first MFN-EP 122 via the input line140, where the transaction identifies a PCI function circuit embedded inthe first MFN-EP 122 corresponding to the second SoC 106. Thetransaction is multiplexed by the first MFN-EP 122 to the appropriatePCI function circuit embedded in the first MFN-EP 122, and that PCIfunction circuit transmits the transaction via the interconnectcommunication bus 130 to the second MFN-EP 124. The second MFN-EP 124then completes the transaction with the second SoC 106 via the outputline 146. The interconnect communication bus 130 may be referred to asan interconnect. In some cases, a response is returned from a SoCdesignated by a transaction to the SoC originating the transaction—forexample, an acknowledgement token or requested data may be returned.

The processor 132 executes computer-readable instructions stored in thememory 134. The memory 134 includes a non-transitory computer readablestorage medium that stores the instructions. The instructions may bestored as software and/or data. The instructions may be stored asfirmware. The processor 132 configures the MFN-EPs 122, 124, 126, 128during initialization of the system 100—for example, managingconfiguration of sizes of memory regions made accessible by SoCs 102,106, 110, 114 and configuration of memory maps.

Turning now to FIG. 2, further details of the MFN-EPs 122, 124, 126, 128are described. The structure of the first MFN-EP 122 presented in FIG. 2is representative of the structure of the MFN-EPs 124, 126, 128. In anexample, each of the MFN-EPs 122, 124, 126, 128 is instantiated from thesame intellectual property core (IP core). An IP core is a block oflogic and/or data that is used in making an application specificintegrated circuit (ASIC) or field programmable gate array (FPGA). Thefirst MFN-EP 122 includes a multiplexing device 170, a first PCIfunction circuit 172, a second PCI function circuit 174, a third PCIfunction circuit 176, and an output address translation unit (ATU) 178.In some contexts, the PCI function circuits 172, 174, 176 may bereferred to as function blocks.

The PCI function circuits 172, 174, 176 correspond to a PCI functionthat the RC 104 may invoke. Each of the PCI function circuits 172, 174,176 includes a plurality of base address registers (BARs) and an inputATU. The first PCI function circuit 172 includes BARs 180 and an inputATU 182, the second PCI function circuit 174 includes BARs 184 and aninput ATU 186, and the third PCI function circuit 176 includes BARs 188and an input ATU 190. In another example, the MFN-EP 122 includes twoPCI function circuits. In another example, the MFN-EP 122 includes fouror more PCI function circuits. In an example, each MFN-EP of the PCIbackplane IC 120 includes a number of PCI function circuits that is oneless than the total number of MFN-EPs in the PCI backplane IC 120. Thefirst PCI function circuit 172 is communicatively coupled to theinterconnect communication bus 130 by a communication path 136-1. Thesecond PCI function circuit 174 is communicatively coupled to theinterconnect communication bus by a communication path 136-2. The thirdPCI function circuit 176 is communicatively coupled to the interconnectcommunication bus by a communication path 136-3. The output ATU 178 iscommunicatively coupled to the interconnect communication bus by acommunication path 136-4.

Each PCI function circuit 172-176 is associated with a specific SoC(e.g., each PCI function circuit 172-176 models a specific SoC to the RC104). For example, the first PCI function circuit 172 is associated to aSoC B, for example the second SoC 106; the second PCI function circuit174 is associated to a SoC C, for example to the third SoC 110; and thethird PCI function circuit 176 is associated to a SoC D, for example tothe fourth SoC 114. Transactions received by the MFN-EP from the RC 104via the input line 140 are parsed by the multiplexing device 170 toidentify which PCI function circuit 172-176 the transaction is directedto (and hence to which SoC the transaction is directed) and then directsthe transaction to the identified one of the PCI function circuits172-176. The PCI function circuit 172-176 uses the BARs 180, 184, 188and the input ATU 182, 186, 190 to map a PCI address associated with thereceived transaction to an address offset and to a reference to an entryin the output ATU of the designated MFN-EP. Only transactions that matchone of the mappings or translations configured into the BARs 180, 184,188 and into the input ATUs 182, 186, 190 are routed by the PCI functioncircuit 172, 174, 176 over the interconnect communication bus. Thus, aSoC 102, 106, 110, 114 can benefit from the transparency provided by thePCI backplane IC 120 to restrict access to its memory by not defining amapping for a specific SoC to its memory or to a specific region of itsmemory.

For example, a transaction designating a PCI address in the PCI addressspace managed by the first RC 104 is directed to the first PCI functioncircuit 172 (and hence to SoC B or to the second SoC 106). The first PCIfunction circuit 172 determines which of the plurality of BARs 180 isreferenced by the PCI address associated with the received transactionand uses that one of the BARs 180 to index into the input ATU 182 tolocate a corresponding local address associating to the output ATU 178of the second MFN-EP 124. The first PCI function circuit 172 establishesa master-slave relationship with the second MFN-EP 124 over theinterconnect communication bus 130 and sends the transaction along withthe local address via the communication path 136-1 to the interconnectcommunication bus 130 and via the interconnect communication bus 130 tothe output ATU 178 of the second MFN-EP 124 over the interconnectcommunication bus 130. In an example, the interconnect communication bus130 may be an electronic crossbar switch or an electronic matrix switch,and the master-slave relationship may be established by configuringswitches in the interconnect communication bus 130. The second MFN-EP124 uses the address offset and the index into the output ATU 178 todetermine a PCI address in the PCI address space managed by the secondRC 108 to which to route the transaction to the second RC 108 of thesecond SoC 106 and sends the transaction via the multiplexing device 170and via the output communication path 146 to the second RC 108 of thesecond SoC 106. In this way, a transaction from the RC 104 istransmitted by an originating SoC to a designated SoC. Further detailsabout how transactions are interconnected among SoCs 102, 106, 110, 114are provided below along with an extended example of configuration ofthe BARs 180, 184, 188, configuration of the input ATUs 182, 186, 190,and the output ATU 178.

Turning now to FIG. 3, further details of one of the BARs 180 aredescribed. While one of the BARs 180 is described here, the other BARsof the BARs 180, the BARs 184, and the BARs 188 have like structures. Aninstance of the BARs 180 includes a memory region size parameter 202 anda PCI address parameter 204. In an example, the instance of the BARs 180includes a region size parameter 202 that may be configured by theprocessor 132 during initialization of the system 100 to contain thesize of a region of memory exported or made accessible by the SoCassociated with the BARs 180 (recall that the BARs 180 are containedwithin a specific one of PCI function circuits 172-176 and the specificPCI function circuit is associated to a specific one of SoCs 102, 106,110, 114). In an embodiment, the PCI backplane IC 120 supports SoCs 102,106, 110, 114 each making accessible up to 1 GB of memory. In anembodiment, the PCI backplane IC 120 supports SoCs 102, 106, 110, 114each making accessible up to a maximum of 2 GB of memory. In anembodiment, the PCI backplane IC 120 supports SoCs 102, 106, 110, 114each making accessible up to a maximum of 5 GB of memory. In anembodiment, the PCI backplane IC 120 supports SoCs 102, 106, 110, 114each making accessible up to a maximum of 10 GB of memory. In anembodiment, one of the SoCs 102, 106, 110, 114 contains one or morememory regions that it makes accessible to one or more of the others ofthe SoCs 102, 106, 110, 114. SoCs 102, 106, 110, 114 can make less thanthe maximum amount of memory accessible. For example, if the PCIbackplane IC 120 supports SoCs 102, 106, 110, 114 each making a maximumof 2 GB of memory accessible, any of those SoCs 102, 106, 110, 114 maymake 10 kB of memory accessible, 100 kB of memory accessible, 1 MB ofmemory accessible, or no memory accessible.

In an embodiment, the MFN-EPs 122, 124, 126, 128 are each configured tocommunicate to an external PCI address space that is a large outboundmemory region containing one or more regions. In an embodiment, theMFN-EPs 122, 124, 126, 128 are each configured to communicate to anexternal PCI address space of a maximum of 1 GB of memory. In anembodiment, the MFN-EPs 122, 124, 126, 128 are each configured tocommunicate to an external PCI address space of a maximum of 2 GB ofmemory. In an embodiment, the MFN-EPs 122, 124, 126, 128 are eachconfigured to communicate to an external PCI address space of a maximumof 5 GB of memory. In an embodiment, the MFN-EPs 122, 124, 126, 128 areeach configured to communicate to an external PCI address space of amaximum of 10 GB of memory.

The PCI address parameter 204 may be configured during initialization ofthe system 100 to associate a PCI address in the PCI address spacemanaged by the RC 104, 108, 112, 116 of the SoC 102, 106, 110, 114 towhich the MFN-EP 122, 124, 126, 128 containing the BARs 180 is coupled(recall that the BARs 180 are contained within a specific one of the PCIfunction circuits 172-176 which is itself contained within a specificone of the MFN-EPs 122, 124, 126, 128, and that specific one of theMFN-EPs 122, 124, 126, 128 is coupled to an RC 104, 108, 112, 116 of aspecific one of the SoCs 102, 106, 110, 114). The PCI address may beprovided and programmed into a BAR of the BARs 180 by the RC 104, 108,112, 116 of the SoC 102, 106, 110, 114 to which the MFN-EP 122, 124,126, 128 containing the BARs 180 is coupled. If the memory region sizeparameter 202 of one of the BARs 180, 184, 188 has a null value or azero value, the processor 132 may not allow provisioning a value intothe PCI address parameter 204 of that BAR. In part, this is a way for aSoC 102, 106, 110, 114 to restrict access to its memory space. If afirst SoC does not provide a value to the memory region size parameter202 of any of the BARs of the PCI function circuit associated with asecond SoC, the second SoC is effectively prohibited from accessing anymemory of the first SoC.

Turning now to FIG. 4, further details of the input ATU 182 aredescribed. While the input ATU 182 is described here, the input ATUs186, 190 have like structures. An input ATU 182 includes a plurality oftranslation registers 210. Each translation register 210 includes alocal address parameter 214. In an example, the translation register 210also includes a BAR identity. The local address parameter 214 identifiesa local address of the PCI backplane IC 120. A local address is anaddress that is unique within a localized address domain, for examplewithin the PCI backplane IC 120. The local address may be associated bythe interconnect communication bus 130 of the PCI backplane IC 120 to aspecific one of the MFN-EPs 122, 124, 126, 128 or to a PCI functionblock within the PCI backplane IC 120. The local address parameter 214may be configured by the processor 132 during initialization of thesystem 100 to associate a specific BAR of the BARs 180 of the PCIfunction circuit of an MFN-EP 122, 124, 126, 128 to a correspondinglocal address of the PCI backplane IC 120. In an example, one of theBARs 180 associates to a translation register 210 by matching the BARidentity of that BAR to the BAR identity of the translation register210. A BAR of the BARs 180 may be statically associated to a translationregister 210 by hardware identity. For example, a first BAR of the BARs180 may be predefined to associate to a first translation register 210in the input ATU 182, and a second BAR of the BARs 180 may be predefinedto associate to a second translation register 210 in the input ATU 182,etc.

Turning now to FIG. 5, further details of the output ATU 178 aredescribed. An output ATU 178 includes a plurality of translationregisters 220. Each translation register 220 includes local addressparameter 222, a PCI address parameter 224, and a size parameter 226.The local address parameter 222 and the PCI address parameter 224 may beconfigured by the processor 132 during initialization of the system 100to associate the local address value stored in the local addressparameter 222 to a PCI address value stored in the PCI address parameter224. The size parameter 226 may be configured by the processor 132during initialization of the system 100 to identify a size of the memoryregion made accessible by the SoC 102, 106, 110, 114 associated to theoutput ATU 178.

In an example, the number of BARs 180 in each PCI function circuit172-176 is 3. In an example, the number of translation registers 210 ineach input ATU 182 is 3. In an example, the number of BARs 180 in eachPCI function circuit 172-176 is 6. In an example, the number oftranslation registers 210 in each input ATU 182 is 6. In an example, thenumber of BARs 180 in each PCI function circuit 172-176 is equal to thenumber of translation registers 210 in each input ATU 182. In anexample, the number of translation registers 220 in each output ATU 178is greater than 12 and less than 96. In an example, the number oftranslation registers 220 in each output ATU 178 is 16. In an example,the number of translation registers 220 in each output ATU 178 is 32. Inan example, the number of translation registers 220 in each output ATU178 is at least 16. To further clarify the use of the BARs 180, the useof the input ATU 182, and the use of the output ATU 178, an extendedexample is provided below.

In an example, the memory 134 of the PCI backplane IC 120 is configuredin advance with data that defines memory regions and sizes of thosememory regions that the SoCs 102, 106, 110, 114 are making accessible.The data also defines to which of the SoCs 102, 106, 110, 114 theregions of memory are accessible. As an example, the memory 134 storesconfiguration data indicating that the first SoC 102 makes a firstregion of memory of 25 Kbytes accessible to the second SoC 106 and tothe third SoC 110, and makes a second region of memory of 80 Kbytesaccessible to the fourth SoC 114. In this example, the configurationdata stored in the memory 134 also indicates that the fourth SoC 114makes a third region of memory of 100 Kbytes accessible to the first SoC102, a fourth region of memory of 150 Kbytes accessible to the first SoC102, a fifth region of memory of 75 Kbytes accessible to the second SoC106, and a sixth region of memory of 125 Kbytes accessible to the secondSoC 106.

By defining translations 210 and 220, access by a second SoC to aspecific memory region in a first SoC can be granted. On the other hand,by not defining a translations 210 and 220, access by the second SoC toa specific memory region in the first SoC can be prohibited. Thetranslations 210 of the input ATUs 182, 186, 190 and the translations220 of the output ATUs 178 of the MFN-EPs 122, 124, 126, 128 promote theadvantage of transparency for SoCs 102, 106, 110, 114 to control accessto their memory regions by other SoCs 102, 106, 110, 114.

In an example, when the PCI backplane IC 120 is powered on, beforecommunication links have been established between the PCI backplane IC120 and the SoCs 102, 106, 110, 114, the processor 132 reads the memoryaccess permissions from the memory 134 and configures the memory regionsize parameters 202 in the appropriate BARs 180, 184, 188 of theappropriate MFN-EPs 122, 124, 126, 128. In this example, the first PCIfunction circuit 172 in each of the MFN-EPs 124, 126, 128 models or isassociated with the first SoC 102, and the third PCI function circuit176 in each of the MFN-EPs 122, 124, 126 models or is associated withthe fourth SoC 114. Given the example of configuration data describedabove, during power on initialization of the PCI backplane IC 120, thememory region size parameter 202 of a BAR of the BARs 180 of the firstPCI function circuit 172 of the second MFN-EP 124 is assigned the valueof 25 Kbytes, the memory region size parameter 202 of a BAR of the BARs180 of the first PCI function circuit 172 of the third MFN-EP 126 isassigned the value of 25 Kbytes, and the memory region size parameter202 of a BAR of the BARs 180 of the first PCI function circuit 172 ofthe fourth MFN-EP 128 is assigned the value of 80 Kbytes. Continuingthis example, the memory region size parameter 202 of a BAR of the BARs188 of the third PCI function circuit 176 of the first MFN-EP 122 isassigned the value of 100 Kbytes, another BAR of the BARs 188 of thethird PCI function circuit 176 of the first MFN-EP 122 is assigned thevalue of 150 Kbytes, the memory region size parameter 202 of a BAR ofthe BARs 188 of the third PCI function circuit 176 of the second MFN-EP124 is assigned the value of 75 Kbytes, and the memory region sizeparameter 202 of another BAR of the third PCI function circuit 176 ofthe second MFN-EP 124 is assigned the value of 125 Kbytes.

After the PCI backplane IC 120 has completed its power oninitialization, the first SoC 102 and/or first RC 104 establishescommunication links with the first MFN-EP 122, the second SoC 106 and/orthe second RC 108 establishes communication links with the second MFN-EP124, the third SoC 110 and/or the third RC 112 establishes communicationlinks with the third MFN-EP 126, and the fourth SoC 114 and/or fourth RC116 establishes communication links with the fourth MFN-EP 128. Duringthis process of establishing communication links, the MFN-EPs 122, 124,126, 128 inform the RCs 104, 108, 112, 116 about the values of thememory region size parameters 202 of BARs 180, 184, 188. In this way,the RCs 104, 108, 112, 116 learn what memory regions and the sizes ofthose memory regions that have been made accessible to them from otherSoCs 102, 106, 110, 114. In the example above, the first RC 104 learnsthat a 100 Kbyte region of memory and a 150 Kbyte region of memory ofthe fourth SoC 114 have been made accessible to it; the second RC 108learns that a 25 Kbyte region of memory of the first SoC 102, a 75 Kbyteregion of memory of the fourth SoC 114, and a 125 Kbyte region of memoryof the fourth SoC 114 have been made accessible to it; the third RC 112learns that a 25 Kbyte region of memory of the fourth SoC 114 has beenmade accessible to it; and the fourth RC 116 learns that an 80 Kbyteregion of memory of the first SoC 102 has been made accessible to it.

Each of the RCs 104, 108, 112, 116, in response to learning what memoryregions and the sizes of those memory regions have been made accessibleto them, allocate PCI addresses in their respective PCI address spacescorresponding to these regions of memory made accessible to them andinform the appropriate one of the PCI function circuits 172, 174, 176 ofthe MFN-EP 122, 124, 126, 128 to which they are communicatively linked.This allocated PCI address is the first in a block of PCI addressesallocated by the RC 104, 108, 112, 116 for communicating to the regionsof memory made accessible, where the number of PCI addresses in theblock is equal to the corresponding memory region size parameter 202 ofthe corresponding BAR of the BARs 180.

In the example above, the first RC 104 assigns the start of the thirdregion of PCI address space (made accessible by the fourth RC 116 to thefirst SoC 102) to PCI address 1000000H (this example value is ahexadecimal number as indicated by the ‘H’ suffix) in the PCI addressspace managed by the first RC 104 and stores 1000000H in the PCI addressparameter 204 of a first BAR of the BARs 188 of the third PCI functioncircuit 176 of the first MFN-EP 122. The first RC 104 maps the start ofthe fourth region of PCI address space (made accessible by the fourth RC116 to the first SoC 102) to PCI address 1020000H in the PCI addressspace managed by the first RC 104 and stores 1020000H in the PCI addressparameter 204 of a second BAR of the BARs 188 of the third PCI functioncircuit 176 of the first MFN-EP 122. In making this mapping, the firstRC 104 leaves enough PCI address space between the 1000000H address andthe 1020000H address to accommodate the size of the third region of PCIaddress space (the 100 Kbytes).

The second RC 108 maps the start of the fifth region of PCI addressspace (made accessible by the fourth RC 116 to the second SoC 106) toPCI address 1000000H in the PCI address space managed by the second RC108 and stores 1000000H in the PCI address parameter 204 of a first BARof the BARs 188 of the third PCI function circuit 176 of the secondMFN-EP 124. The second RC 108 maps the start of the sixth region of PCIaddress space (made accessible by the fourth RC 116 to the second SoC106) to PCI address 1020000H in the PCI address space managed by thesecond RC 108 and stores 1020000H in the PCI address parameter 204 of asecond BAR of the BARs 188 of the third PCI function circuit 176 of thesecond MFN-EP 124. In making this mapping, the second RC 108 leavesenough PCI address space between the 1000000H address and the 1020000Haddress to accommodate the size of the fifth region of PCI address space(the 75 Kbytes). The second RC 108 maps the start of the first region ofPCI address space (made accessible by the first RC 104 to the second SoC106 and to the third SoC 110) to PCI address 1040000H in the PCI addressspace managed by the second RC 108 and stores 1040000H in the PCIaddress parameter 204 of the first BAR of the BARs 180 of the first PCIfunction circuit 172 of the second MFN-EP 124.

The third RC 112 maps the start of the first region of PCI address space(made accessible by the first RC 104 to the third SoC 110 and to thesecond SoC 106) to PCI address 1000000H in the PCI address space managedby the third RC 112 and stores 10000000H in the PCI address parameter204 of the first BAR of the BARs 180 of the first PCI function circuit172 of the third MFN-EP 126. The fourth RC 116 maps the start of thesecond region of PCI address space (made accessible by the first RC 104to the fourth SoC 114) to PCI address 8000000H in the PCI address spacemanaged by the fourth RC 116 and stores 8000000H in the PCI addressparameter 204 of the first BAR of the BARs 180 of the first PCI functioncircuit 172 of the fourth MFN-EP 128.

The example addresses above are arbitrary and different addresses couldhave been used in the examples. Note that the PCI address parameter 204value (1040000H) of the first BAR of the BARs 180 of the first PCIfunction circuit 172 of the second MFN-EP 124 is different from the PCIaddress parameter 204 value (1000000H) of the first BAR of the BARs 180of the first PCI function circuit 172 of the third MFN-EP 126, eventhough these two PCI address parameters 204 are associated to the samefirst region of the PCI address space controlled by the first RC 104.This illustrates the independence between the PCI address spaces managedby each of the separate RCs 104, 108, 112, 116.

The memory 134 of the PCI backplane IC 120 may also be configured withaddresses the RCs 104, 108, 112, 116 associate to the memory regionsthey make accessible to other SoCs 102, 106, 110, 114. During power oninitialization of the PCI backplane IC 120, the processor 132 may readthese addresses from the memory 134 and configure these addresses intothe PCI address parameter 224 of translations register 220 in the outputATUs 178 of the subject MFN-EPs 122, 124, 126, 128. A local addressvalue of the PCI backplane IC 120 can be assigned by the processor 132to the local address parameter 222 of this translation register 220associated to the memory region, and the same local address value can beassigned by the processor 132 to the local address parameter 214 of acorresponding translation register 210 in the input ATU 182, 186, 190 ofthe corresponding one of the PCI function circuits 172, 174, 176 of theappropriate MFN-EP 122, 124, 126, 128 (e.g., MFN-EPs that are associatedto SoCs 102, 106, 110, 114 that have been granted access to the memoryregion). In an alternative example, the RCs 104, 108, 112, 116 caninform the PCI backplane IC 120 during communication link establishmentof the PCI addresses to associate to memory regions made accessible bySoCs 102, 106, 110, 114, and the processor 132 can configure thetranslation registers 220, 210 at that time.

Continuing the example give above, the PCI backplane IC 120 isconfigured in advance with data indicating the first RC 104 associatesPCI address 3000000H with the first memory region it makes accessible tothe second SoC 106 and the third SoC 110 and associates PCI address3080000H with the second memory region it makes accessible to the fourthSoC 114. The PCI backplane IC 120 is configured in advance with dataindicating the fourth RC 116 associates PCI address 3000000H with thethird memory region it makes accessible to the first SoC 102, PCIaddress 3040000H with the fourth memory region it makes accessible tothe first SoC 102, PCI address 3080000H with the fifth memory region itmakes accessible to the second SoC 106, and PCI address 3060000H withthe sixth memory region it makes accessible to the second SoC 106. Notethat both the first RC 104 and the fourth RC 116 associate memory madeaccessible to duplicate PCI addresses (3000000H and 3080000H are used byboth the first RC 104 and the fourth RC 116), but this is allowedbecause they are PCI addresses in PCI address spaces independentlycontrolled by each RC respectively.

The PCI backplane IC 120 associates a local address of 183000000H to thePCI address 3000000H and a local address of 183080000H to the PCIaddress 3080000H of the first RC 104. The PCI backplane IC 120associates a local address of 303000000H to the PCI address 3000000H, alocal address 303040000H to the PCI address 3040000H, a local address303080000H to the PCI address 3080000H, and a local address 303060000Hto the PCI address 3060000H of the fourth RC 116. Note that the PCIbackplane IC 120 associates different local addresses to the PCI address3000000H of the first RC 104 and the PCI address 3000000H of the fourthRC 116 and different local addresses to the PCI address 3080000H of thefirst RC 104 and the PCI address 3080000H of the fourth RC 116.

The PCI backplane IC 120 configures a first translation register 220 ofthe output ATU 178 of the first MFN-EP 122 to store 183000000H in itslocal address parameter 222 and to store 3000000H in its PCI addressparameter 224. This first translation register 220 corresponds to thefirst memory region made accessible by the first SoC 102 to the secondSoC 106 and to the third SoC 110. The PCI backplane IC 120 configures asecond translation register 220 of the output ATU 178 of the firstMFN-EP 122 to store 183080000H in its local address parameter 222 and tostore 3080000H in its PCI address parameter 224. This second translationregister 220 corresponds to the second memory region made accessible bythe first SoC 102 to the fourth SoC 114. The PCI backplane IC 120configures a first translation register 210 of the input ATU 182 of thefirst PCI function circuit 172 of the second MFN-EP 124 to store183000000H in its local address parameter 214 and configures a firsttranslation register 210 of the input ATU 182 of the first PCI functioncircuit 172 of the third MFN-EP 126 to store 183000000H in its localaddress parameter 214. The first translation register 210 of the inputATU 182 of the first PCI function circuit 172 of the second MFN-EP 124associates to the first BAR of the BARs 180 of the first PCI functioncircuit 172 of the second MFN-EP 124. The first translation register 210of the input ATU 182 of the first PCI function circuit 172 of the thirdMFN-EP 126 associates to the first BAR of the BARs 180 of the first PCIfunction circuit 172 of the third MFN-EP 126. The PCI backplane IC 120configures a first translation register 210 of the input ATU 182 of thefirst PCI function circuit 172 of the fourth MFN-EP 128 to store183080000H in its local address parameter 214. The first translationregister 210 of the input ATU 182 of the first PCI function circuit 172of the fourth MFN-EP 128 associates to the first BAR of the BARs 180 ofthe first PCI function circuit 172 of the fourth MFN-EP 128.

The PCI backplane IC 120 may configure the interconnect communicationbus 130 to route communication directed to local addresses extendingfrom 180000000H to 1FFFFFFFFH to the first MFN-EP 124. The PCI backplaneIC 120 may configure the interconnect communication bus 130 to routecommunication directed to local addresses extending from 200000000H to27FFFFFFFH to the second MFN-EP 124. The PCI backplane IC 120 mayconfigure the interconnect communication bus 130 to route communicationdirected to local addresses extending from 280000000H to 2FFFFFFFFH tothe third MFN-EP 126. The PCI backplane IC 120 may configure theinterconnect communication bus 130 to route communication directed tolocal addresses extending from 300000000H to 37FFFFFFFH to the fourthMFN-EP 128. In another example, the PCI backplane IC 120 may configurethe interconnect communication bus 130 to route communications accordingto a different scheme of local address routing than the example providedabove.

The PCI backplane IC 120 configures a first translation register 220 ofthe output ATU 178 of the fourth MFN-EP 128 to store 303000000H in itslocal address parameter 222 and to store 3000000H in its PCI addressparameter 224. The PCI backplane IC 120 configures a second translationregister 220 of the output ATU 178 of the fourth MFN-EP 128 to store303040000H in its local address parameter 222 and to store 3040000H inits PCI address parameter 224. The PCI backplane IC 120 configures athird translation register 220 of the output ATU 178 of the fourthMFN-EP 128 to store 303080000H in its local address parameter 222 and tostore 3080000H in its PCI address parameter 224. The PCI backplane IC120 configures a fourth translation register 220 of the output ATU 178of the fourth MFN-EP 128 to store 3030130000H in its local addressparameter 222 and to store 30130000H in its PCI address parameter 224.

The PCI backplane IC 120 configures a first translation register 210 ofthe input ATU 190 of the third PCI function circuit 176 of the firstMFN-EP 122 to store 303000000H in its local address parameter 214 andconfigures a second translation register 210 of the input ATU 190 of thethird PCI function circuit 176 of the first MFN-EP 122 to store303040000H in its local address parameter 214. The first translationregister 210 of the input ATU 190 of the third PCI function circuit 176of the first MFN-EP 122 associates to the first BAR of the BARs 188 ofthe third PCI function circuit 176 of the first MFN-EP 122, and thesecond translation register 210 of the input ATU 190 of the third PCIfunction circuit 176 of the first MFN-EP 122 associates to the secondBAR of the BARs 188 of the third PCI function circuit 176 of the firstMFN-EP 122.

The PCI backplane IC 120 configures a first translation register 210 ofthe input ATU 190 of the third PCI function circuit 176 of the secondMFN-EP 124 to store 303080000H in its local address parameter 214 andconfigures a second translation register 210 of the input ATU 190 of thethird PCI function circuit 176 of the second MFN-EP 124 to store3030130000H in its local address parameter 214. The first translationregister 210 of the input ATU 190 of the third PCI function circuit 176of the second MFN-EP 124 associates to the first BAR of the BARs 188 ofthe third PCI function circuit 176 of the second MFN-EP 124, and thesecond translation register 210 of the input ATU 190 of the third PCIfunction circuit 176 of the second MFN-EP 124 associates to the secondBAR of the BARs 188 of the third PCI function circuit 176 of the secondMFN-EP 124.

When the BARs 180, 184, 188, the translations register 210 of the inputATUs 182, 186, 190, and the translations register 220 of the output ATUs178 of the MFN-EPs 122, 124, 126, 128 have been initialized andconfigured as described above, the PCI backplane IC 120 is ready toroute transactions among SoCs 102, 106, 110, 114. An example, using theexemplary configurations described above, of transaction routing is nowdescribed.

During operation of the system 100, the SoC 102 sends a transaction viathe first RC 104 over the input communication path 140 to PCI address1000000H to the first MFN-EP 122. This PCI address 1000000H isassociated with the first BAR of the BARs 188 of the third functioncircuit 176 of the first MFN-EP 122, and is the first address in theassociated block of PCI addresses. This PCI address is mapped by theinput ATU 190 of the third function circuit 176 of the first MFN-EP 122to the local address 303000000H. The third function circuit 176 of thefirst MFN-EP 122 sends the transaction onto the interconnectcommunication bus 130 directed to the local address 303000000H. Theinterconnect communication bus 130 routes this to the fourth MFN-EP 128.The fourth MFN-EP 128 finds a translation register 220 in its output ATU178 that maps this local address 303000000H to the PCI address 3000000H.The fourth MFN-EP 128 then sends the transaction to the fourth RC 116directed to PCI address 30000000H.

The examples above illustrate how SoCs 102, 106, 110, 114 can makeregions of their memories accessible to specific other one of the SoCs102, 106, 110, 114—granting access to some of SoCs 102, 106, 110, 114and restricting access to others of SoCs 102, 106, 110, 114. Thisexample also illustrates how the PCI address space of one RC 104, 108,112, 116 can be translated by the PCI backplane IC 120 to the PCIaddress space of a different RC of RCs 104, 108, 112, 116. This approachprovides many advantages over the alternative interconnect technologieswhich may not support the ability to restrict access to SoCs 102, 106,110, 114 one-by-one (e.g., allow access to a first region of PCI addressspace to a first SoC and restrict access to the first region to a secondSoC and to other SoCs and allow access to a second region of PCI addressspace to a second SoC and restrict access to the second region to thefirst SoC and other SoCs).

Turning now to FIG. 6A and FIG. 6B, another example of a PCI backplaneIC 121 is described in the context of the system 400. In an example, thePCI backplane IC 121 includes a first multifunction endpoint (MFN-EP)123, a second MFN-EP 125, a third MFN-EP 127, the interconnectcommunication bus 130, the processor 132, the memory 134, and a localfunction circuit 135. The PCI backplane IC 121 shares a number of thesame structures as the PCI backplane IC 120, and these like structuresoperate similarly to the corresponding structures of the PCI backplaneIC 120. The local function circuit 135 provides some processingdirectly, rather than shunting a transaction to a SoC 102, 106, 110 forprocessing. The local function circuit 135 may be an acceleratorprocessing function. The local function circuit 135 may be an on-chipperipheral. The local function circuit 135 may be an IP block.

With reference now to FIG. 6B, each MFN-EP 123, 125, 127 has a fourthPCI function circuit 177 that receives transactions addressed by the RC104 to the local function circuit 135 and transmits the transaction viaa communication path 136-5 to the interconnect communication bus 130,and via the interconnect communication bus 130 to the local functioncircuit 135 for processing. In an example, the PCI backplane IC 121includes two or more local function circuits 135 and two or moreMFN-EPs, where each of the MFN-EPs includes a number of PCI functioncircuits 177 that match the number of local function circuits 135. Notethat because PCI transactions inherently identify a function, there isno need to translate an address for the PCI backplane IC 121 to routethe transaction to the local function circuit 135.

Turning now to FIG. 7A and FIG. 7B, a method 300 of communicatingbetween different peripheral component interconnect root complexes (PCIRCs) is described. The sequence of steps of method 300 span FIG. 7A andFIG. 7B. With reference to FIG. 7A, at block 302, the method 300includes reading a plurality of memory region configuration definitionsby a processor of a backplane integrated circuit (IC) (e.g., processor132 of PCI backplane IC 120, 121), where each memory regionconfiguration definition identifies a size of a memory region,identifies an IC communicatively coupled to the backplane IC where thememory region is located, and identifies another IC communicativelycoupled to the backplane IC allowed access to the memory region, whereeach IC (e.g., SoCs 104, 106, 110, 114) is communicatively coupled to adifferent multi-function endpoint (MFN-EP) (e.g., MFN-EPs 122, 124, 126,128, 123, 125, 127) of the backplane IC. In an example, the backplane ICis the PCI backplane IC 120, 121. In an example, the processor 132 readsthe memory configuration definitions from the memory 134. In an example,the processor 132 reads the memory configuration definitions from memoryexternal to the backplane IC.

At block 304, the method 300 includes, for each IC (e.g., SoCs 104, 106,110, 114) allowed access to one of the memory regions, writing the sizeof the memory region by the processor in a base address register (BAR)of a peripheral component interconnect (PCI) function circuit of theMFN-EP coupled to the IC. For every memory region exported by an IC, thesize of the memory region is programmed by the processor 132 into one ormore of the BARs 180, 184, 188 of the corresponding one of the PCIfunction circuits 172, 174, 176 that models the IC that is making thememory region accessible to the IC to which one of the PCI functioncircuits 172, 174, 176 is associated.

At block 306, the method 300 includes, for each IC where a memory regionis located (e.g., a memory region that a SoC 102, 106, 110, 114 ismaking accessible to another of the SoCs), configuring a translationregister (e.g., translation register 120) of an output addresstranslation unit (ATU) (e.g., ATU 178) in the MFN-EP (e.g., one ofMFN-EPs 122, 124, 126, 128, 123, 125, 127) coupled to the IC by theprocessor (e.g., processor 132) with a local address local to thebackplane IC (e.g., PCI backplane ICs 120, 121) and with an addressmanaged by a PCI RC (e.g., one of RCs 104, 108, 112, 116) of the IC. Theprocessing of block 306 can be decomposed as two parts: (A) allocating alocal address local to the backplane IC for this memory region madeaccessible by the IC and (B) configuring the translation register of theATU in the MFN-EP coupled to the IC.

At block 308, the method 300 includes, for each IC allowed access to oneof the memory regions (e.g., one of the memory regions that a SoC 102,106, 110, 114 is making accessible to another of the SoCs), configuringa translation register (e.g., translation register 210) of an input ATU(e.g., one of input ATUs 182, 186, 190) in the PCI function circuit(e.g., one of the PCI function circuits 172, 174, 176, 177) of theMFN-EP coupled to the IC by the processor with a local address local tothe backplane IC where the translation register of the input ATU isassociated to the BAR of the PCI function circuit of the MFN-EP.

At block 310, the method 300 includes, for each IC allowed access to amemory region (e.g., a memory region that a SoC 102, 106, 110, 114 ismaking accessible to another of the SoCs), receiving a PCI addressmanaged by a PCI RC (e.g., one of PCI RC 104, 108, 112, 116) of the ICby the MFN-EP coupled to the IC and configuring the PCI address into theBAR of the PCI function circuit of the MFN-EP coupled to the IC.

With reference now to FIG. 7B, at block 312, the method 300 includesreceiving a PCI transaction by an MFN-EP designating a PCI functioncircuit of the MFN-EP, where the PCI transaction includes a PCI addressin the PCI address space managed by the PCI RC of the IC coupled to theMFN-EP, where the PCI function circuit is associated to an IC where amemory region is located to which the IC coupled to the MFN-EP isallowed access.

At block 314, the method 300 includes looking up a BAR of the PCIfunction circuit by the PCI function circuit based on the PCI address inthe PCI transaction. At block 316, the method 300 includes reading thetranslation register associated to the looked up BAR of the PCI functioncircuit by the PCI function circuit. At block 318, the method 300includes determining a local address based on the translation registerand the PCI address in the PCI transaction by the PCI function circuit.

At block 320, the method 300 includes transmitting the PCI transactionby the PCI function circuit to the local address via an interconnectcommunication bus of the backplane IC. At block 322, the method 300includes routing the PCI transaction by the interconnect communicationbus (e.g., interconnect communication bus 130) to the MFN-EP coupled tothe IC where the memory region is located. At block 324, the method 300includes transmitting the PCI transaction by the MFN-EP coupled to theIC where the memory region is located to the PCI RC of the IC where thememory region is located.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. An integrated circuit, comprising: aninterconnect communication bus; and a peripheral component interconnect(PCI) multi-function endpoint (MFN-EP) coupled to the interconnectcommunication bus, the MFN-EP comprising: a first address translationunit (ATU); and a PCI function circuit, wherein the PCI function circuitcomprises: base address registers (BARs) comprising a selected BAR,wherein the selected BAR is associated with an address internal to theintegrated circuit associated with the first ATU; and a second ATU;wherein the PCI function circuit is configured to: receive a transactionassociated with a PCI address; determine that the PCI address isassociated with the selected BAR; and using the selected BAR and thesecond ATU, determine an address internal to the integrated circuitbased on the PCI address.
 2. The integrated circuit of claim 1, furthercomprising a local PCI function circuit coupled to the interconnectcommunication bus.
 3. The integrated circuit of claim 2, wherein thelocal PCI function circuit is an accelerator processing function.
 4. Theintegrated circuit of claim 1, further comprising a processor coupled tothe interconnect communication bus.
 5. The integrated circuit of claim4, wherein the processor is configured to execute instructions thatcause the processor to configure the first ATU and the second ATU bywriting values to the first ATU and the second ATU.
 6. The integratedcircuit of claim 1, wherein the PCI function circuit comprises BARs. 7.The integrated circuit of claim 1, wherein the integrated circuitcomprises 4 MFN-EPs.
 8. The integrated circuit of claim 1, wherein thefirst ATU comprises at least 16 translation registers.
 9. The integratedcircuit of claim 1, wherein the MFN-EP is configured to communicate withan external PCI address space of at least 1 GB extent.
 10. A methodcomprising: reading memory region configuration definitions, by aprocessor of a backplane integrated circuit (IC), wherein each memoryregion configuration definition identifies a size of a memory region,identifies an IC communicatively coupled to the backplane IC where thememory region is located, and identifies another IC communicativelycoupled to the backplane IC allowed access to the memory region, whereineach IC is communicatively coupled to a different multi-functionendpoint (MFN-EP) of the backplane IC; for each IC allowed access to oneof the memory regions, writing the size of the memory region by theprocessor in a base address register (BAR) of a peripheral componentinterconnect (PCI) function circuit of the MFN-EP coupled to the IC; foreach IC where a memory region is located, configuring a translationregister of an output address translation unit (ATU) in the MFN-EPcoupled to the IC by the processor with a local address local to thebackplane IC and with an address managed by a PCI root complex (RC) ofthe IC; and for each IC allowed access to one of the memory regions,configuring a translation register of an input ATU in the PCI functioncircuit of the MFN-EP coupled to the IC by the processor with a localaddress local to the backplane IC wherein the translation register ofthe input ATU is associated to the BAR of the PCI function circuit ofthe MFN-EP.
 11. The method of claim 10, further comprising for each ICallowed access to a memory region, receiving a PCI address managed by aPCI RC of the IC by the MFN-EP coupled to the IC and configuring the PCIaddress into the BAR of the PCI function circuit of the MFN-EP coupledto the IC.
 12. The method of claim 11, comprising receiving a PCItransaction by an MFN-EP designating a PCI function circuit of theMFN-EP and comprising a PCI address in a PCI address space managed bythe PCI RC of the IC coupled to the MFN-EP, wherein the PCI functioncircuit is associated to an IC where a memory region is located to whichthe IC coupled to the MFN-EP is allowed access; looking up a BAR of thePCI function circuit by the PCI function circuit based on the PCIaddress in the PCI transaction; reading the translation registerassociated to the looked up BAR of the PCI function circuit by the PCIfunction circuit; determining a local address based on the translationregister and the PCI address in the PCI transaction by the PCI functioncircuit; transmitting the PCI transaction by the PCI function circuit tothe local address via an interconnect communication bus of the backplaneIC; routing the PCI transaction by the interconnect communication bus tothe MFN-EP coupled to the IC where the memory region is located; andtransmitting the PCI transaction by the MFN-EP coupled to the IC wherethe memory region is located to the PCI RC of the IC where the memoryregion is located.
 13. The method of claim 10, wherein the backplane ICcomprises 4 MFN-EPs.
 14. An integrated circuit, comprising: aninterconnect communication bus; and a peripheral component interconnect(PCI) multi-function endpoint (MFN-EP) coupled to the interconnectcommunication bus, the PCI MFN-EP comprising: a multiplexing deviceadapted to be coupled to a first system on a chip (SoC), themultiplexing device configured to direct a transaction from the firstSoC to the PCI function circuit responsive to determining that thetransaction is for a second SoC; a first address translation unit (ATU);and a PCI function circuit coupled to the multiplexing device, the PCIfunction circuit configured to model the second SoC, the PCI functioncircuit comprising: a second ATU; and base address registers (BARs). 15.The integrated circuit of claim 14, further comprising a local functioncircuit coupled to the interconnect communication bus.
 16. Theintegrated circuit of claim 15, wherein the local function circuit is anaccelerator processing function.
 17. The integrated circuit of claim 14,comprising a processor coupled to the interconnect communication bus.18. The integrated circuit of claim 17, wherein the processor isconfigured to execute instructions that cause the processor to configurethe first ATU and the second ATU of the MFN-EP.
 19. The integratedcircuit of claim 14, wherein the integrated circuit comprises 4 MFN-EPs.20. The integrated circuit of claim 14, wherein the MFN-EP comprisesthree PCI function circuits.